NACA-RM-L54E19 REV A

Abstract

INTRODUCTION <br>The design of the internal-flow system of a turbojet-powered aircraft for optimum operation at transonic or supersonic speeds tends to compromise the operation of the system at conditions corresponding to take-off and low-speed operation (i.e., extremely high mass-flow ratios at or very near choking and thus possibly large performance losses).Effort has been made to avoid this low-speed performance penalty in practice by means of auxiliary inlets or by variable &#8211;geometry inlets. It would be desirable, of course, to avoid such mechanical complication by the design of a fixed-geometry system having high performance characteristics at mass-flow ratios near the theoretical maximum. However, little information is available on the effects of inlet geometry on static or low-speed performance (refs. 1 to 5), and, since a transonic inlet investigation in the Langley 8-foot transonic tunnel has made available several 8-inch-diameter subsonic, transonic, and supersonic air inlets of varying proportions and lip profiles, it was considered that a study of the internal performance of these inlets at static conditions might be useful in indicating some of the more important effects of inlet geometry. Although the inlets available did not embody a systematic variation of isolated geometric variables, they do afford a wide range of the variables of lip roundness, inlet area, and diffusion rate and magnitude. Although the inlets available did not embody a systematic variation of isolated geometric variables, they do afford a wide range of the variables of lip roundness, inlet area, and diffusion rate and magnitude. Accordingly, static induction tests of several of these inlets were conducted on a suction test stand at the Langley 8-foot transonic tunnel. <br>In this paper the results of the static-condition investigation of six NACA 1-series nose inlets (one with protruding central body) are reported and compared with other data available. Total-pressure surveys and pressure-recovery measurements were made through a mass-flow range extending from below the normal operating range to choking. In addition, flow-visualization studies were made of some of the inlets by utilizing the tuft and the liquid-film-flow techniques.